<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script type="text/javascript">
		// 传递实参了实参的值是多就是多少，如果没有传递实参(当前是undefined)使用默认值
			function fn(a=1,b=2){
				console.log(a+b);
			}
			
			fn(10,20);
			fn();
			
			
			let fn1 = (a=10,b=20)=>{
				console.log(a,b);
			}
			
			fn1();
			fn1(undefined,100);
		</script>
	</body>
</html>
